The conventional papermaking machine includes a press section having one or more pairs of cooperating press rolls and the wet paper web is supported on a papermaker's felt as it passes through the nip between the cooperating rolls, thereby extracting water from the web. After leaving the press section, the paper web is transferred to the dryer section which can consist of a plurality of heated dryer rolls. The paper web passes sequentially around the dryer rolls to remove further moisture from the paper.
In some installations, there is a substantial draw or span between the press section and the dryer section. The paper web is fairly wet and heavy, so that the web can sag in this draw and possibly break. A papermaking machine can be operating at a speed in the neighborhood of 2,000 ft. per minute, and if the web breaks, the paper web must be re-fed through the entire press and dryer sections and this not only results in a loss of product, but also results in substantial downtime for the papermaking machine.
Sag in the draw between the press section and the dryer section can be minimized by increasing the tension on the paper web, but an increase in tension will correspondingly tend to stretch the paper web and increase the tendency for breakage.
A dryer section of a conventional papermaking machine may include about ten to twelve steam heated dryer rolls or cylinders, commonly referred to as cans, and the first or upstream roll in the section, to which the wet paper web is transferred from the press section of the machine, is at a lower temperature than other downstream rolls. In practice, the upstream dryer roll will have a surface temperature of approximately 140.degree. F. to 150.degree. F., and the surface temperature of the next several downstream rolls will be progressively increased to a value of approximately 280.degree. F. to 325.degree. F., and this higher surface temperature will then be maintained throughout the remaining rolls of the series. By maintaining the temperature of the first dryer roll at a lower value, possible blistering and delamination of the paper web is prevented, and the lower temperature will also eliminate the tendency of the paper web to adhere to the roll.